A short-acting cycloplegic and mydriatic drug is:

Correct Answer: D

Rationale: The correct answer is D: Tropicamide. Tropicamide is a short-acting cycloplegic and mydriatic drug commonly used in ophthalmology. It acts quickly, providing temporary dilation of the pupil and relaxation of the ciliary muscle for refraction assessment. Atropine (A) is a long-acting cycloplegic, not short-acting. Homatropine (B) and Hyoscine (C) are also longer-acting drugs compared to Tropicamide. Therefore, D is the correct answer for its rapid onset and short duration of action in dilating the pupil and paralyzing accommodation.

Correct Answer: C

Rationale: The correct answer is C: Phenylephrine. Phenylephrine is a sympathomimetic drug that stimulates the sympathetic nervous system, leading to vasoconstriction and increased heart rate. In contrast, choices A, B, and D all work to depress sympathetic activity by different mechanisms. Clonidine is an alpha-2 adrenergic agonist that decreases sympathetic outflow. Reserpine inhibits the storage of norepinephrine, leading to decreased sympathetic activity. Labetalol is a non-selective beta blocker that blocks beta-adrenergic receptors, reducing sympathetic effects. Therefore, Phenylephrine is the only drug among the options that does not depress sympathetic activity.

Correct Answer: C

Rationale: Cocaine blocks the reuptake of noradrenaline from adrenergic nerves, leading to excessive stimulation of adrenergic receptors. This causes increased blood pressure, which can result in a hypertensive crisis or stroke. Additionally, the vasoconstrictive effects of excess noradrenaline can lead to tissue damage in the nose when cocaine is inhaled frequently. Choices A and B are incorrect because cocaine does not directly block alpha adrenergic or muscarinic receptors. Choice D is incorrect because cocaine does not deplete norepinephrine from adrenergic nerve endings but rather increases its concentration by blocking reuptake.

Correct Answer: A

Rationale: The correct answer is A: "Don't stop taking this medication without a doctor's advice first." Abruptly stopping a β-blocker can lead to severe adverse reactions like rebound hypertension, angina exacerbation, or arrhythmias due to sudden withdrawal. This instruction is crucial to prevent these potentially dangerous consequences. Explanation for why other choices are incorrect: B: β-blockers are not known to commonly cause urinary frequency, so this warning is unnecessary. C: Blurred vision is not a common side effect of β-blockers, so this warning is irrelevant. D: While constipation can be a side effect of some medications, it is not a prominent side effect of β-blockers, so this advice is not essential for patients taking β-blockers.

Correct Answer: D

Rationale: The correct answer is D because removing hawks would lead to an increase in both grasshoppers and rabbits. Hawks are natural predators of both grasshoppers and rabbits. With fewer hawks preying on them, the populations of grasshoppers and rabbits would increase due to reduced predation pressure. Choice A is incorrect because the removal of hawks would lead to an increase in grasshoppers and rabbits, not no change. Choice B is incorrect because removing hawks would not cause a decrease in grasshoppers but rather an increase. Choice C is incorrect because the removal of hawks would actually result in an increase in the populations of both grasshoppers and rabbits, not no change.